Lewis selected as his first assistant, and to act as leader in case of his own disability or death, William Clark, four years his senior, and a brother of George Rogers Clark, who had captured Kaskaskia, Cahokia, and the Illinois country, and otherwise distinguished himself. Strangely enough, in his mental and moral qualities William Clark was almost a duplicate of Meriwether Lewis. Throughout the whole of the hazardous, difficult, toilsome journey that was now begun, the two men were most devoted friends, Lewis having not the slightest fear that Clark would receive too much credit, and neither having the least jealousy of the other; quite in contrast with some expeditions of later years, where the leader must be all in all. The result was that the world to-day exalts all the more this noble commander-in-chief because his broad generosity forever linked with his, almost as a single name, that of his subordinate officer, so that the great undertaking is not the Lewis, but the Lewis and Clark, expedition. Clark was to have a commission as captain, but when it came it proved to be merely lieutenant. He took it, never grumbled, and, when he returned, gave the commission back. As far as the head of the Missouri apparently they would traverse no absolutely new ground, for as has been noted the Frenchmen had been from the Mandan villages to the eastern slopes of the Rocky Mountains, and from the French-Spanish settlement of St. Louis numbers of trappers and traders had gone to the Mandan country, while the chief road to that region had long been from the north-east by way of the lakes, and the Assiniboine where the British fur companies had established trading-posts. From these points their traders reached the natives of the upper Missouri and Mississippi, which territory the British claimed as their own. Charles Chaboillez, one of the chief factors of the North-west Company, was in charge of Montagne à la Basse, situated on the Assiniboine probably about where the Verendryes' Fort la Reine had been. From here he and other traders often went to the Mandan country to deal with various natives who made that region a rendezvous. He had proposed to Daniel Harmon that they should make a journey from the Mandan towns west to the Rocky Mountains,[65] over the course the Mandans "pursued every spring to meet and trade with another tribe ... which resides on the other side of the Rocky Mountain." This expedition was never undertaken, but it indicates the degree of familiarity possessed by the Mandans with the Western country, and shows how the earlier Frenchmen found their way out at least as far as the Yellowstone, already known as the Roche Jaune, a name which in itself is a suggestion of early French visitors to the great falls of that stream where the gorgeous yellow colouring is so remarkable. Peter Fidler, another of the British fur traders, had been down from the Saskatchewan through the area drained by the headwaters of the Missouri. A trader